Plastic films are widely used for magnetic tapes and optical members such as flat panel displays, as well as food packages, film capacitors, and other applications, and such plastic film products are ultimately wound into a film roll body by a winder for shipment.
A plastic film may undergo corona discharge surface treatment in a part of the film conveyance process as a pre-process for secondary processing such as bonding on a film surface, as described in Patent Literature 1. In Patent Literature 1, a film runs on the grounded conveyance roller called counter electrode roller, and an electrode, provided at a position opposed to the roller with the film interposed, applies alternating current (AC) high voltage to the electrode surface-side of the film for discharge treatment. A nip roller is installed at a position where the film comes into contact with the counter electrode roller, in order that the counter electrode roller contact surface-side of the film is not treated by discharge when the electrode surface-side of the film is subjected to the discharge treatment. The pressing force by the nip roller prevents a large amount of air from intruding into the gap between the counter electrode roller and the film and prevents discharge treatment on the counter electrode roller contact surface-side of the film.
In the manufacturing process for plastic films, when the width and the speed are increased to improve the productivity of films, vibration of the counter electrode roller and the nip roller increases to deform the rubber coating on the surface of the nip roller and change the roller cross section from a perfect circle into a polygonal shape. The reason for this phenomenon is that resonance occurs even though the rotation frequency of the roller is initially controlled in a frequency range lower than the first-order eigen frequency of the roller alone and the first-order eigen frequency of the entire apparatus. The frequency observed at this moment is an integer multiple (N times) of the rotation frequency, and the matching of this frequency with the eigen frequency causes continuous resonance, which gradually deforms the roller surface into a polygonal shape having N vertices.
This problem will be examined in terms of a method of manufacturing a film roll body. For example, in the aforementioned corona treatment unit, much air intrudes between the film and the counter electrode roller in polygon cycles, resulting in a defect of unintended, periodic corona discharge treatment on the counter electrode roller surface.
Another problem similar to this is an angular deformation phenomenon in a press roll for dewatering in a paper machine in a papermaking process as disclosed in Patent Literature 2. This angular deformation phenomenon is described as resonance caused when a frequency N times the rotation frequency of the top roller and the bottom roller included in the press roller system matches the eigen frequency of a press roller apparatus replaced with a vibration model of a multi-degree of freedom system, and this phenomenon is thought to be similar to the polygonal deformation phenomenon as described above. As an approach to the phenomenon, it is proposed to change the diameters of the top roller and the bottom roller such that the outer diameter ratio between these rollers is not 1, so as to prevent a match with the eigen frequency assumed from a frequency N times the rotation frequency. This approach avoids a perfect match between an integer multiple of the rotation frequency and the eigen frequency and avoids resonance, thereby preventing polygonal deformation.
Similarly, as another approach to the press roller polygonal deformation phenomenon in paper machines, Patent Literature 3 avoids vibration between rollers at a particular frequency by continuously varying the operating speed and preventing the same parts in rubber members on the surfaces of the rollers from being pressed with a large pressure, thereby preventing or retarding polygonal deformation. It is also suggested that the time to avoid a resonance point is increased by fluctuating the speed.